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1. Methods of analysing the spatial patterns of birds are reviewed. Few methods have sought to explain an observed spatial pattern in terms of the behavioural responses between conspecifics. The spacing of oystercatchers, Haematopus ostralegus L., feeding on a mussel bed is investigated using a model of one possible response. 2. The model assumes that each individual avoids all other individuals within a certain distance, the hard-core radius, and has no interaction with other individuals beyond this distance. 3. The positions of the oystercatchers are obtained from a set of photographs. Each photograph is transformed to a plan view, and the resulting set of plan views is assembled to give the spatial pattern of birds on the mussel bed. The observed spatial pattern is summarized by means of the distribution of nearest-neighbour distances. 4. The behaviour of the birds is modelled by placing non-overlapping particles of a given radius within the region of the mussel bed occupied by the birds. The distribution of nearest-neighbour distances for the particles is obtained by simulation. The best-fitting particle radius is that which minimizes the residual error between the observed and simulated distributions of nearest-neighbour distances. 5. Statistical analyses show that avoidance behaviour, as measured by the best-fitting particle radius, decreases during the low-water period. We interpret this result in terms of the changing value of a food item to an individual through time.

Seedling trees of Argyrodendron sp., A. trifoliolaturn, Flindersia brayleyana and Toona australis were grown for c. 180 days under one of three light regimes with either of two nutrient levels (6 treatments in all). Light regimes spanned the range of environmental conditions which these species would normally experience in northern Queensland rainforest: deep shade (1.3 mol quanta m-2 day-1, equivalent to forest floor), moderate light (5.6 mol quanta m-2 day-1, comparable to midcanopy), and strong light (23 mol quanta m-2 day-1, matching daily irradiance of exposed crowns). Long-term shade tolerance in Argyrodendron sp. and A. trifoliolaturn was associated with limited responses in growth and leaf anatomy to low light and nutrients. Starch accumulation in leaves under all treatments, and especially low nutrients, implied that supply of photoassimilate exceeded demand. Such a conservative carbon economy, plus the accumulation of stem P reserves, even in a weak light environment, is consistent with a protracted existence as part of a forest floor community. By contrast, shade-intolerant Toona is an early successional species and lacks such adaptive features. Instead, light and nutrients had a strong interactive effect on growth. Flindersia, with a broad tolerance to sun and shade, was intermediate in growth response and leaf adjustment, which is consistent with its success across a wide size range of forest gaps.

Species with contrasting shade tolerance were grown under three light by two nutrient treatments. Gas exchange by intact leaves, leaf disk O2 evolution and chlorophyll fluorescence were measured. In shade-tolerant evergreen species (Argyrodendron sp., A. trifoliolatum and Flindersia brayleyana) photosynthetic activity of seedlings in air at light saturation (A) was lower under weak (30 pmol quanta m-2 day-1 ), compared with medium (130) or strong light (535). In Toona australis, a shade-intolerant and deciduous tree, A was reduced 44% from strong to weak light treatment on high nutrients (71 mg N L-1 nutrient solution). Nevertheless, nitrogen-use efficiency for leaf photosynthesis was highest in Toona under all growing conditions and, with higher specific leaf area, probably contributes towards fast occupancy of sites which underlies early succession in this species. All species made photosynthetic and respiratory adjustments from strong to medium to weak light, which resulted in a lower light compensation point (Q0). Such adjustments were accentuated by low nutrient supply (1.0 mg N L-1 nutrient solution) and were especially pronounced for shade-intolerant Toona. Reduced Q0 in Toona was accompanied by lower A and light saturation point (QA). Both species of Argyrodendron showed no decrease in QA despite reduction in Q0 under weak light.Contrary to expectation, photosynthetic responses to light × nutrient treatments did not correlate with degree of shade tolerance accorded each species by rainforest ecologists.

Seed from four species of rainforest trees with widely contrasting sunlight requirements for growth and development were sown within disturbance gaps amidst mature forest on the Herberton Range in North Queensland. Observations on seedling persistence plus comparative growth of young trees of Acacia aulacocarpa, Toona australis, Flindersia brayleyana and Darlingia darlingiana (species ranked according to adaptation from full sun to deep shade) confirmed a broad tolerance of Flindersia to sunlight under all conditions, from wide to narrow gaps (minimum 0.6% full sun equivalent). Photosynthetic attributes which underlie such broad tolerance were subsequently inferred from single leaf gas exchange, plus foliar analyses of nitrogen, phosphorus and chlorophyll on tree seedlings held for 180 days under two nutrient × three irradiance levels adjusted to represent natural irradiance incident upon the forest floor (low), mid-canopy (medium) and emergent crowns (high irradiance treatment). Medium irradiance plus high nutrients proved optimal for leaf expansion, chlorophyll content and photosynthesis in air. Growth under low irradiance was characterised by thinner leaf palisade tissue, lower rates of dark respiration, increased leaf chlorophyll per unit nitrogen and lower light compensation point for photosynthesis. Such leaves retained a relatively high photosynthetic capacity despite these other shade-leaf attributes. High irradiance plus low nutrients proved supraoptimal for leaf expansion and expression of photosynthetic activity. Chronic photoinhibition appeared to prevail because apparent quantum yield was reduced, while photosynthetic processes on a nitrogen basis were substantially impaired. Nitrogen use efficiency, as inferred from leaf chlorophyll content, light saturated CO2 assimilation rate, electron transport rate and carboxylation rate on a nitrogen basis declined with increasing growth irradiance. Some ecological implications for the establishment and growth of these rainforest tree species in disturbance gaps are discussed.